From the Barnard website:
"A student who has completed 24-60 credits at another institution is considered a transfer applicant. If you anticipate completing fewer than 24 credits, you MUST apply as a first-year student. The number of transfer credits accepted by Barnard will be determined by the Office of the Registrar and students will be notified of their credit status at the time of admission."
Barnard College Admissions : Applying
So, as long as she stays under those 60 credits, the amount of time won't make her ineligible. Will the new grades erase the lower one's, though?